Field of the Invention
The present invention relates to an Aspergillus mutant strain suitable for solid culture and also suitable as a host for genetic transformation and a transformant obtained from the Aspergillus mutant strain.
Description of the Related Art
Conventionally, a method for manufacturing alcohol such as ethanol by saccharizing lignocellulosic biomass, such as rice straw and corn stover, as a substrate using a saccharifying enzyme and fermenting the resulting sugars by microorganisms (alcohol-fermenting microorganisms) is known.
It is known that transformants into which a saccharifying enzyme gene has been introduced into Aspergillus strains such as Aspergillus oryzae are used when the lignocellulosic biomass is saccharized with a saccharifying enzyme. For example, the transformants are solid cultured by using the lignocellulosic biomass to produce the saccharifying enzyme, so that the lignocellulosic biomass is saccharized with the saccharifying enzyme.
However, because Aspergillus oryzae has protease genes and produces proteases, it has a problem in that a heterologous enzyme produced by the transformant may be degraded by the proteases.
To solve the problem, it is known that deletion of protease genes of Aspergillus oryzae will enhance production of the heterologous enzyme (see e.g., Disruption of ten protease genes in the filamentous fungus Aspergillus oryzae highly improves production of heterologous proteins, Appl Microbiol Biotechnol (2011) 89: 747-759).
However, an Aspergillus oryzae deficient in one or more protease genes cannot sufficiently enhance production of the heterologous enzyme. Therefore, further improvements are desired.